Polymers vary widely in their resistance to burning. Some, such as the polyolefins, polystyrene, polyalkyl acrylates and methacrylates, polyvinyl acetate and the like, burn readily. Polytetrafluoroethylene, polyvinylidene chloride and polyvinyl chloride, on the other hand, have a rather high resistance to burning. In any event, it obviously is highly desirable that, for certain applications, a polymer should have a high degree of flame-retardance so that it will meet safety standards imposed by government regulation on the manufacture of toys, carpeting, drapery materials, automotive parts, etc.
The treatment of the more flammable polymers to increase their resistance to burning is well known; such treatment generally has involved the incorporation in the polymer composition of substantial proportions of antimony oxide, halogenated hydrocarbons and low molecular weight phosphate esters. Ordinarily, though, the effective use of these and other additives has required their presence in such high concentrations as to adversely affect the desirable properties of the polymer. Thus, such desirable properties as hardness, clarity, strength, elasticity, etc., are diminished significantly by the presence of large amounts of a flame-retardant chemical.
The formulator's goal, in preparing a flame-retardant polymer composition, is to add just enough of the flame-retardant compound so as to provide the desired degree of flame-retardance, but no more than this minimum amount, so as to preserve as much as possible the advantageous properties of the polymer. Frequently, it is not possible to select a flame-retardant which will meet these requirements satisfactorily.
As noted earlier herein, the flame-retardant properties of the polymer compositions are provided by certain phosphorus- and halogen-containing acids.
The preparation of 2,2-di(chloromethyl)trimethylene hydrogen phosphate by reaction of 2,2-di(chloromethyl)trimethylene glycol with polyphosphoric acid at 100.degree. C. is shown in "Simple Syntheses of Cyclic Phosphate Esters" by A. M. Meston, J. Chem. Soc., 1963 (Dec.), 6059. The reaction required 16 hours.
U.S. Pat. No. 2,661,365 (Gamrath et al.) shows in very general terms the hydrolysis (with water) of alkanediol phosphoryl monochlorides to yield the corresponding alkanediol phosphoric acids. The alkanediol nucleus is a substituted trimethylene glycol residue wherein the substituents are alkyl groups.
The hydrolysis of 2-chloro-5,5-dimethyl-2-oxo-1,3,2-dioxaphosphorinane with aqueous acetone is shown in "Cyclic Organophosphorus Compounds-III" by R. S. Edmundson, Tetrahedron, 21 (9), 2379-87 (1965), at page 2384. The hydrolysis mixture is heated over steam for 1.5 hours and the product is the corresponding phosphoric acid.